I know that repeating a statement time and again, and evading or brushing off any challenge to its truthfulness, can make themselves leaders of public opinion — and thus more able to achieve their political objectives.

Perhaps the most glaring current example of this practice is Gov. Peter Shumlin’s repeated declaration that $1 spent now on universal preschool education saves the taxpayers anywhere from $7 to $14 “down the road.” President Obama also repeated that 7:1 claim in his state of the union address, where he like Shumlin called for more billions in preschool expenditures.

At a July 25 news conference at Washington County Family Services, Shumlin offered the “$12 to $14 return” version of this claim. True North Reports’ Kevin P. Ryan asked Shumlin what studies he had to back up such a claim.

Shumlin confidently replied, “Every reasonable study, that I have read, and I suspect that everyone at this press conference has ever read, suggests that there’s a direct correlation between early intervention, early services and those children and a bright future.”

Curious about the governor’s claim of scholarship, the Ethan Allen Institute sent him a polite letter a few days later asking him to identify any “reasonable” studies that he had read “that support your assertion about the astonishing savings from investing in universal preschool education.”

A month later the governor’s special assistant Susan Bartlett gave us a reply. It was perfectly clear to us that neither Peter Shumlin nor Susan Bartlett had ever read any study that concluded that universal preschool education produced any sort of “savings down the road.” We can say that confidently because we have read a great deal of the research, and if there were such a study it would be a bombshell.

The advocates’ most common claim for savings is the number reported by the foundation researchers who evaluated the 1962 to 1965 Perry Preschool Program. It was emphatically not “universal preschool.” It was a study of 58 seriously at risk inner city minority children with IQs between 70 and 85, from dysfunctional families in Ypsilanti, Michigan.

And the program was a lot more than four hours a day of “preschool.” The children were selected because they had parents at home during the day, so the preschool aides could make home visits. The researchers arrived at the return on investment ($7.16 on $1 expended) by counting as “savings” the fact that by age 19 only 33 percent had dropped out of high school, only 31 percent had been arrested, and only 17 of the 25 girls had become pregnant.

To take such findings and proclaim that universal preschool in Vermont or any state will produce a 7:1 return — not to mention the 16:1 sometimes claimed — is, to put it as mildly as possible, dishonest.

There have been two longitudinal studies of statewide universal preschool programs. Georgia State University concluded that 10 years of Georgia’s universal preschooling had consumed $1.15 billion but produced no observable educational achievement. In Oklahoma, there were some behavioral benefits, but the state’s fourth grade reading scores had declined six years after universal preschool began in 1998.

Last December the Department of Health and Human Services released its long-delayed Head Start Impact Study, covering 5,000 “disadvantaged” three- and four-year olds and 84 sponsoring agencies. The key finding: “There was little evidence of systematic differences in children’s elementary school experiences through 3rd grade, between children provided access to Head Start and their counterparts in the control group.”

“In terms of children’s well-being, there is also clear evidence that access to Head Start had an impact on children’s language and literacy development while children were in Head Start. … However, these early effects rapidly dissipated in elementary school, with only a single impact remaining at the end of 3rd grade for children in each age cohort.”

Taxpayer-financed universal preschooling does produce some benefits. It expands the shrinking public school population. It also drives independent day care centers toward extinction. The educational bureaucrats like that.

It sustains the need for more certified public school teachers. The teachers’ union likes collecting their dues.

It offers “free” day care to working families.

Many families and employers — particularly the Vermont Business Roundtable and its partner “Corporate Voices for Working Families” — like that.

It puts three- and four-year-olds into the custody of certified child rearing experts, who believe they can remedy the deficiencies of the children’s parents.

It spreads the available funding over all children, at the expense of the 10 percent who could actually benefit from focused help.

By promoting spending for universal preschool, politicians like Peter Shumlin can gain political support from all these interests — so long as no one challenges their deceptive claims.

What universal preschool does not do is produce any lasting educational benefit for either ordinary or needy children, and certainly little or no return for taxpayers called upon to foot the ever rising costs.